Resistance penetration

Resistance penetration is a property of hits that reduces the target's effective resistance to specific damage types.

Mechanics

When a target is struck by a hit with resistance penetration, that target's effective resistance is reduced for determining the amount of damage dealt by the hit. Resistance penetration does not modify the target's resistance or maximum resistance stats.

The target's effective resistance to damage type $\color[RGB]{163,141,109} t$ is

$$\color[RGB]{163,141,109} R_t = \min( r_t, m_t ) - p_t$$ where $\color[RGB]{163,141,109} r_t$ is the target's resistance to damage type $\color[RGB]{163,141,109} t$, $\color[RGB]{163,141,109} m_t$ is the target's maximum resistance to damage type $\color[RGB]{163,141,109} t$, and $\color[RGB]{163,141,109} p_t$ is the resistance penetration of the hit for damage type $\color[RGB]{163,141,109} t$.

Just like resistance stats, effective resistance can be a negative number. There is no minimum limit on effective resistance imposed by the game mechanics.

Due to the fact that resistance penetration is a property of hits, it cannot apply to damage over time.

Additionally, if a target's resistances are ignored—for example, via the armor The Eternity Shroud or the keystone Inevitable Judgement—penetration also has no effect, and the relevant resistance is treated as zero.

Efficacy of resistance penetration versus resistances

Efficacy of 10% resistance penetration versus resistances

It can be shown that resistance penetration is more effective in terms of damage dealt against targets with higher resistances.

The percentage increase to damage type $\color[RGB]{163,141,109} t$ as a result of resistance penetration is

$$\color[RGB]{163,141,109} I_t = \frac{ p_t }{ 1 - \min( r_t, m_t ) }$$

Sources of resistance penetration

Currently, resistance penetration exists only for elemental damage types.

'Damage Penetrates x% Fire Resistance' on weapon affects player's skills and spells, not minions (Source: PoB).

Items

Other items

• can add Damage Penetrates 5% Elemental Resistances during any Flask Effect to belts.
• Elder sceptres and wands can have Socketed Gems are Supported by Level (16-20) Fire Penetration.
• Shaper weapons and amulets can have Damage Penetrates (4–10)% Elemental Resistances.
• can have following modifiers:
  • Damage Penetrates (10-15)% Fire Resistance while affected by Anger
  • Damage Penetrates (10-15)% Cold Resistance while affected by Hatred
  • Damage Penetrates (10-15)% Lightning Resistance while affected by Wrath